Optical films having a high refractive index layer have been described. Such optical films can be used as an intermediate construction in an antireflective (“AR”) film. AR films are often constructed of alternating high and low refractive index (“RI”) layers of the correct optical thickness. With regards to visible light, one example is a thickness on the order of one-quarter of the wavelength of the light to be reflected. The human eye is most sensitive to light around 550 nm. Therefore, it is desirable to design the low and high index coating thicknesses in a manner that minimizes the amount of reflected light (e.g. 2.5% or lower) at around 550 nm.
As described for example in U.S. Patent Publication US2007/0286994, in order to reduce or eliminate optical fringing, it is preferred that the antireflective film substrate has a refractive index close to that of the high refractive index layer, i.e. differs from the high refractive index layer by less than 0.05, and more preferably less than 0.02. Further, a primer can be provided on the film substrate, the primer being chosen to closely match the refractive index of the high refractive index layer and the substrate.
Primers have also been employed to improve adhesion. When a primer is applied at a low coating thickness, of for example 30 nm, the primer does not substantially affect the optical fringing or the antireflective properties.